Various techniques have been devised to inspect the inside of an interior space, such as a coating hopper used in the application of aqueous or solvent solutions to a moving substrate. Coating hoppers used in the manufacture of sensitized products, such as photographic film and photographic paper, generally have narrow slots through which solution passes prior to being applied to a web or roll. A typical coating hopper (FIG. 1), such as described in U.S. Pat. No. 4,287,240, assigned to Eastman Kodak Co., comprises a substantially rectangular body portion 1 having a slot 2 formed between two substantially rectangular bars 3,4. The slot length (L) is defined as the distance from the cavity (C) to the slide surface (S). The width of the hopper slot is the distance from one end of the hopper to the other or the length of the bars 3,4. In operation, the solution contained in the hopper (FIG. 1) is distributed through the hopper slot 2, onto the hopper slide subface (S) and, onto the web or roll to be coated. Obstructions in the slot of the hopper can result in localized widthwise nonuniformities in the delivery of the solution to the web or roll. The localized widthwise nonuniformity can be of great enough magnitude that it would be considered a defect in the web coating and the web would have to be scrapped. Thus, the cleanliness of the slots of the "coating hoppers" is critical in the manufacture of defect free web coatings.
One such method of inspecting a coating hopper environment involves the use of a hand held light source and a thin piece of transparent plastic material. In this method, the inspector holds the plastic material over a hopper slot while water is delivered through the hopper slot. The inspector then positions the light source over the hopper slot. The transparent material together with the running water enables light to be directed into the slot. The inspector then peers through the transparent material to examine the slot for particulate or foreign objects. Another technique also involves the use of a hand held light source and a transparent plastic material. In this technique, the inspector inserts the plastic material into the hopper slot (with or without water running through the hopper slot) and again positions the light source and his or her eyes over the slot. The light source illuminates the edge of the plastic material to provide a glowing surface which acts as a light source to illuminate the hopper slot. The inspector must position the light source at the correct angle to assure proper illumination of the slot. The inspector must then position his/her eye over the hopper slot to peer into the slot.
The problem with the prior art techniques and apparatus for inspecting a slot is the inherent difficulty in performing the inspection. Prior art techniques require that the inspector hold, angle, or position a plastic material and a light source while simultaneously orienting his/her eye over the hopper slot. Thus, the result of having any one of these items out of alignment creates a potential for not identifying particulate matter that may be present in the slot of the hopper. Other shortcomings of the prior art techniques include the presence of reflections and the inability to distinguish between the reflections and the actual slot. Moreover, the task of inspecting using existing devices is also quite time consuming because of the complexity of aligning the various elements of the inspection as indicated above, i.e., the plastic, light source, and inspector's eye. Consequently, the foregoing shortcomings of prior art inspection methods invariably result in residual particulates or contaminants in the hopper slot that result in a localized widthwise nonuniformity in the web coating.
The device of Van Slyke, U.S. Pat. No. 3,718,814, is one such attempt to provide a fiber optic illuminator for remote inspection. Van Slyke depends on the illuminator emitting light laterally of the axis of the bundle where the illuminator is desired. This arrangement, however, does not permit illumination of the entire work area because there is no axial transmission of light.
Accordingly, there persists a need for an inspection method and apparatus therefor that obviates the shortcomings of the prior art techniques, and in particular, one that enables the inspector to fully inspect all regions of the hopper environment.